1. Field of the Invention
The present invention relates to an ink for ink-jet recording which makes it possible to obtain vivid recorded matters by satisfying both of the prevention of the feathering and the prevention of the bleeding even when the recording is performed on regular paper.
2. Description of the Related Art
In the ink-jet recording system, ink droplets are formed by means of the ink discharge method including, for example, the electrostatic attraction method, the method in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element or the like, and the method in which bubbles are generated by heating the ink to utilize the pressure generated thereby. All or a part of the ink droplets are adhered to a recording objective material such as paper to perform the recording. Those usable as the ink for ink-jet recording to be used for the ink-jet recording system as described above include those which are obtained by dissolving or dispersing a variety of water-soluble dyes or pigments in water or a liquid medium composed of water and a water-soluble organic solvent.
In order to perform the satisfactory recording over a long period of time, for example, it is required for the ink for ink-jet recording as described above that characteristic values including, for example, the viscosity, the surface tension, and the density have appropriate values, that any deposit is not formed and/or physical values are not changed, for example, by the heat in order to avoid any clog-up at the nozzle and the orifice of the recording apparatus so that the ink is discharged in a stable manner, and that the recorded image is excellent, for example, in water resistance and weather resistance.
When the recording is performed with an ink-jet printer by using a general ink for ink-jet recording, any exclusive ink-jet paper is sometimes used in order to obtain a satisfactory printing quality without any blurring. However, in recent years, it is more demanded that the recording is performed on the regular paper rather than on the exclusive ink-jet paper, in consideration of the running cost and the environment. Further, in the market directed to homes and offices, it is overwhelmingly demanded that the recording is performed with the colors rather than with the black-and-white or monochrome. Therefore, the color ink-jet printer is dominantly used. It is demanded that the color recording can be performed with a good printing quality on the regular paper.
However, the printing quality on the regular paper is still insufficient. Major factors therefor may include the following two factors. One is the problem called “feathering”. In this case, the ink is nonuniformly blurred along the surface of the recording paper when the ink is permeated into the recording paper. The edges of image portions are notched, and it is impossible to obtain any sharp edge of the image portion. The other is the problem called “bleeding”. In this case, inks having different colors are mixed with each other at boundary portions between those having different colors. The both inks are blurred, and the printing quality is deteriorated.
In view of the above, many techniques have been hitherto used in order to avoid the feathering and the bleeding so that the printing quality is improved. A method, in which the surface tension is increased, is widely known as a general technique for avoiding the feathering. For example, Japanese Patent Application Laid-open No. 8-259864 discloses a technique in which the surface tension of an ink is made to be not less than 40 mN/m so that the blurring is suppressed and the feathering is avoided. However, in this method, the permeation of the ink into the paper is slow. Therefore, the bleeding tends to occur on the paper surface.
On the other hand, those widely used as a general technique for avoiding the bleeding include a method in which alkyl ether of polyvalent alcohol such as diethylene glycol monobutyl ether is blended as a permeating agent to an ink and/or a surfactant is blended. For example, Japanese Patent Application Laid-open No. 8-283631 discloses a technique in which a specified permeating agent and a surfactant are blended to an ink to lower the surface tension and enhance the permeability into the paper so that the bleeding is avoided. However, in this method, the feathering tends to occur.
As described above, the conventional inks for ink-jet recording have involved such a problem that it is difficult to satisfy both of the prevention of the feathering and the prevention of the bleeding on the regular paper.